import java.util.HashMap;
import java.util.List;
import java.util.Map;

class Etl {

    Map<String, Integer> transform(Map<Integer, List<String>> old) {
        Map<String, Integer> result = new HashMap<>();

        old.forEach(
                (i, list) -> list.forEach(
                        s -> result.put(s.toLowerCase(), i)
                )
        );

        return result;
    }
}
